Breeding of the Korean Native Bumblebee, Bombus ignitus Queens Hyung Joo Yoon*, Kyeong Yong Lee, Mi Ae Kim, and In Gyun Park Department of Agricultural Biology, National Academy of Agricultural Science, RDA, Suwon 441-100, Korea *To whom correspondence should be addressed. Department of Agricultural Biology, National Academy of Agricultural Science, RDA, Suwon 441-100, Korea. Tel: +82-31-290-8567; E-mail: [email protected] Running title : Breeding of the bumblebee Bombus ignitus Abstracts Many bumblebee species have declined in number in recent decades, particularly in developing regions. Widespread declines of bumblebee species threaten the pollination levels of both wildflowers and crops. Here, we investigated the body weight and colony-developmental characteristics of Korean native bumblebee (B. ignitus) queens collected from 2000 to 2010 for conservation of native bumblebees for breeding. The average weight of 6,852 queens was 0.77 ± 0.44 g. The weight of B. ignitus queens collected in 2005 was the greatest, 0.87 ± 0.12 g, which was 1.0–1.3- fold heavier than any other year. The average oviposition rate was 81.6 ± 10.7%, and 2004 showed the highest rate, 95.0%. This value corresponded to 1.1-1.6-fold increases over the queens collected in the other years. The average rate of colony foundation was 60.9 ± 11.0%. Queens in 2008 exhibited the best performance, 75.4%, which was 1.0-1.9-fold higher than the other years. The rate of progeny-queen production averaged 27.0 ± 9.4% and peaked in 2001 at 43.2%; this value was 1.1– 4.7-fold higher than other years. The average number of queens produced and number of generations begotten by queens was 27.6 ± 10.1% and 4.8 ± 2.0, respectively. Queens in 2000 averaged 9 generations of offspring, which was 1.1-3.1-fold greater than other years. These results indicate that the colony-developmental characteristics of the collected queens changed significantly between 2000 and 2010. In addition, there was no correlation between body weight and number of queens collected, although body weight was affected by collection year. Since 2008, the colony- developmental characteristics of queens have worsened. Key words: Bumblebee, Bombus ignitus, Breeding, Colony development, Generation. 2 Introduction Bees are diverse and abundant, with 16,325 species identified throughout the world (Michener, 2000). Arguably, the most important activity of bees is their pollination of natural vegetation and agricultural plants. Pollination is an ecosystem service in that wild pollinators, in particular wild bees, contribute significantly to the pollination of a large array of crops (Morandin and Winston, 2005; Greenleaf and Kremen, 2006; Winfree et al., 2007). Commercially managed bees are also available for pollination services and are used in large commercial fields, small gardens, or enclosures such as greenhouses and screen houses (Free, 1993; Dag and Kammer, 2001). The introduction of bumblebees into greenhouses for pollination has become widespread in recent years, and demand increases annually. Bumblebees provide farmers the opportunity to decrease their pollination labor costs and promise a good crop yield, both in quantity and in quality (reviewed by Velthuis and van Doorn, 2006). It has been estimated that the bumblebees sold in 2004 consisted of approximately 930,000 colonies of the Eurasian Bombus terrestris, approximately 55,000 colonies of the North American B. impatiens, and a few thousand colonies each of the Eurasian B. lucorum, East Asian B. ignitus, and North American B. occidentalis (Velthuis and van Doorn, 2006). The large bumblebee B. terrestris is naturally distributed in Europe and adjacent territories, including England, most of Scotland, the north coast of Africa, southern Scandinavia, major Mediterranean islands, and some Atlantic islands (Madeira and the Canary Islands) (Estoup et al., 1996; Chittka et al., 2004; Velthuis and van Doorn, 2006). Since 1987, B. terrestris has been available commercially in portable boxes for crop pollination (Mitsuhata, 2000). Colonies of B. terrestris have 3 been imported into many countries, including Korea, Japan, China, Taiwan, Mexico, Chile, Argentina, Uruguay, South Africa, Morocco, and Tunisia (Dafni, 1998). It has been attempted to substitute Korean native bumblebees for foreign bumblebees. Out of seven Korean native bumblebees tested, B. ignitus showed the best results both in artificial multiplication and in pollinating ability, and it was selected as the most reliable native species for crop pollination (Yoon et al., 1999). In this study, we examined the breeding characteristics of B. ignitus queens that had been collected from 2000 to 2010 in various locations in Korea under indoor rearing for conservation of native bumblebees. Materials and Methods Collection of post-hibernated queens The post-hibernated queens of the Korean native bumblebee, Bombus ignitus, visiting mainly the blossom of Corydalis speciosa (Fumariaceae) and Prunus yedoensis, were collected in many localities, including Jeong-Sun, Gang-Won do, Korea, during the spring seasons of 2000 to 2010. The number of bumblebees collected in the spring seasons of 2000 to 2010 was 713, 170, 80, 865, 949, 404, 1,147, 713, 407, 752 and 653, respectively. The collected B. ignitus queens were weighed before the start of indoor rearing. Indoor rearing The collected queens were reared in three types of cardboard (1.5 mm thick) boxes, respectively, for nest initiation (10.5×14.5×6.5 cm), colony foundation (21.0×21.0×15.0 cm), and colony maturation (24.0×27.0×18.0 cm). Each box had a wire net window on its lid for ventilation. The sizes of these windows were 5.5×6.5 4 cm, 7.0×14.0 cm and 10.0×20.0 cm, respectively. Queens collected in the field were first confined individually in small boxes for colony initiation and remained there until oviposition. When the adults emerged from the first brood, the nest was transferred to a medium box for colony foundation and left there until the number of workers reached 50. The nest was then moved to the large box for further colony development. A 40-50% sugar solution and pollen dough were provided ad libitum. The pollen dough was made from 40-50% sugar solution and fresh pollen collected from an apiary (v:v = 1:1). Frequency distribution of the body weight of founder B. ignitus queens We investigated the frequency distribution of the body weight of founder B. ignitus queens collected from 2000 to 2010. We classified founder queens into seven weight classes: below 0.5 g (below 0.59 g), 0.6 g (0.60-0.69 g), 0.7 g (0.70-0.79 g), 0.8 g (0.80-0.89 g), 0.9 g (0.90-0.99 g), 1.0 g (1.0-1.99 g), and over 1.1 g (over 1.10 g). The number of bumblebees collected was 713 in 2000, 170 in 2001, 80 in 2002, 865 in 2003, 949 in 2004, 404 in 2005, 1,147 in 2006, 713 in 2007, 407 in 2008, 752 in 2009, and 653 in 2010. Statistical analyses Statistical analyses were conducted using Tukey’s HSD post-hoc test following a one-way ANOVA Welch and chi-square test (MINITAB Release 13 for Windows, 2000). Tukey’s pairwise comparison test was used to examine the weight of B. ignitus queens collected in 2000 to 2010. The chi-square test was used to compare the rates of colony oviposition, colony foundation, production of progeny-queen, number of progeny-queen per queen, and number of offspring generations. 5 Results and Discussion Comparison of body weights of collected founder B. ignitus queens To investigate the correlation between the body weight and developmental characteristics of B. ignitus, we weighed B. ignitus queens collected in 2000 to 2010 (Fig. 1). The average weight of the 6,852 queens was 0.77 ± 0.44 g. The weight of B. ignitus queens collected in 2005 was the greatest, 0.87 ± 0.12 g, which was 1.0–1.3- fold heavier than queens collected in other years. The weight of B. ignitus queens collected in 2003 was the lowest, 0.68 ± 0.11 g. There was a significant difference in the weights of queens collected in different years (one-way ANOVA Welch test, Tukey’s HSD post-hoc test: F=162.732, df1=10, df2=1,375.433, p=0.0001). For the frequency distribution of the collected queens, we classified founder queens into seven weight classes ranging from below 0.5 g to over 1.1 g (Fig. 2). Among these weight classes, the 0.6 g class was the most prevalent in queens collected in 2003, 2004 and 2006 (30.8%-37.2%); the 0.7 g class was the most prevalent in queens collected in 2001 and 2008 (29.5%-32.7%); and the 0.8 g class was the most prevalent in queens collected in 2000, 2005, 2007, 2009 and 2010 (26.2%-32.5%). The below 0.5 g class was more common in 2003 (22.5%) than in any other year, and 2005 had the highest prevalence of the over 1.1 g class (5.0%). The weight of 364 queens of B. terrestris collected in another study averaged 0.829 ± 0.141 g and ranged from 0.4 g to 1.2 g (Beekman et al., 2000). Although the shape of the frequency distribution of the weights of those B. terrestris queens was similar to that of the 6,852 B. ignitus queens collected during the present study in Korea, the post-hibernated queens of B. ignitus weighed slightly less than B. terrestris. Body size is one of the most important life-history characteristics of an organism 6 (Calder, 1984; Schmidt-Nielsen, 1984; Roff, 1992).